Silence the last two C4996 warnings in our code

hook_registry.cpp still used strncpy for the hook-name copy (the same
class the log-ring fix addressed) -- replace with a bounded memcpy.
coop_vk_layer.cpp's debug logger used _wfopen -- switch to _wfopen_s.
Both were the only remaining C4996s in our own code.

vk_layer/coop_vk_layer.cpp

@@ -151,8 +151,8 @@ void logvk(const char* fmt, ...)
 	if (GetTempPathW(MAX_PATH, dir) == 0) {
 		return;
 	}
-	FILE* f = _wfopen((std::wstring(dir) + L"coop_vk_layer.log").c_str(), L"a");
-	if (f == nullptr) {
+	FILE* f = nullptr;
+	if (_wfopen_s(&f, (std::wstring(dir) + L"coop_vk_layer.log").c_str(), L"a") != 0 || f == nullptr) {
 		return;
 	}
 	va_list ap;